In order for a circuit that generates a signal and a circuit driven by the signal to be separate with respect to potential, it is customary to use a potential barrier in the form of a magnetically coupled coil pair for signal transmission and energy transfer. The time-variable magnetic field of the coil pair switches between the galvanically separate circuits or system regions. One or more input coils function for each individual signal transmission as senders of the signal. The signal is coupled, by the magnetic field of the coil pair, to one or more coils that are instantaneously not emitting, which are used for signal reception (so-called output coils or receiver coils). One suitable circuit configuration on the output side or the receiver side extracts the originally sent signal, or rather its information content, from the output signal of the output coil.
In the case of the transmission of a two-valued signal, the emitted signal can include a continuous signal, a modulated signal and especially a pulse train or a single pulse. Single or a plurality of uncorrelated single pulses are usually emitted (FIGS. 2 and 4, uppermost signature) at a distance from one another that is long compared to the pulse duration.
Methods are known from US Patent Application 2005/0156699 A1 and Patent Document EP 0 935 263 B1 in which a coil pair is driven at a frequency at which the impedance of a coil pair equivalence circuit has its maximum and which is less than the resonant frequency of the coil pair. A larger number of exciting cycles from the sender side is required.
In the method of pulse pause modulation, in which the signal to be transmitted is coded two-valued or more-valued in the switch-on time and the switch-off time of continuously sent rectangular function, a large number of exciting cycles on the sender side is required (S. Zeltner, M. Billmann, M. März, E. Schimanek, “A compact IGBT driver for high temperature applications”, Proceedings PCIM 2003, pages 211 to 216).
A method is known from U.S. Pat. No. 6,262,600 B1 in which a periodic signal is generated for the transmission of a two-valued signal via a potential barrier, whose frequency takes on two different values, depending on the frequency of the instantaneous level of the signal to be transmitted. Signals A simultaneous transmission of signal and energy via a common channel is possible using this method, just as in the case of the pulse-pause modulation method and the method depending on the resonant frequency of the coil pair. However, the methods lead to a high power loss, and the demodulation on the receiver's side requires the processing of a certain minimum number of signal cycles. This causes a delay in the transmission, as well as a certain uncertainty of the delay time (so-called jitter). The delay time can be reduced by raising the modulation frequency within the technical limits of the overall system. However, this can result in a further increase in the power loss.
If the single pulses are not sent in the form of a closed signal sequence, such as a sine wave, a rectangular function or the like, but separately from one another, the distance between the single pulses can be uniform, for example, (homogeneous pulse sequence) or the distance in time between respectively two subsequent pulses can be nonuniform, in that it increases with increasing distance in time from the preceding level change of the signal that is to be transmitted (DE 102 28 543 A1).
A transmission method is known from US Patent Application 2004/0101036 A1, in which a first channel and a second channel are used for the transmission. An announcing signal which includes at least one pulse is transmitted over the first channel. A data signal is transmitted within a time window over the second channel, the time window being open for a prescribed time duration after the announcing signal. The data signal can thereby be distinguished from possible interference signals. However, an additional expenditure on the system side is required, by making available two independent channels. Furthermore, interferences which occur after the time window has been opened and before it closes again are not filtered out, but can possibly affect the data signal. The wider the time window, the higher is the probability of the appearance of interferences. The probability of interference can be reduced by sending the data signal repeatedly.
A transmission method having one channel is known from US Patent Application 2003/0151442 A1, which incorporates the properties of the magnetically coupled coil pair used as transmitter. The slopes of the signal to be transmitted are converted to short pulses. Each pulse can be sent repeatedly to improve the security from interference. The magnetic transmitter translates the primary side pulses into the corresponding pulses on the secondary side. The maximum working frequency of the electronic circuit that drives the magnetic transformer is below the latter's working frequency range. For each pulse on the primary side there is a corresponding sequence of two pulses on the secondary side, the polarities of the pulses on the secondary side being reverse to one another. In the case of secondary pulses that appear in rapid succession, or in case of the simultaneous appearance of separate secondary pulses, an evaluation circuit prevents the passing along of the secondary pulses to a storage element.
In power electronics systems, transient voltages frequently occur between the primary and the secondary side, that is, between the input and the output side of a magnetic transformer (so-called dU/dt interferences). The time duration of these interferences is usually greater than the duration of the pulses on the secondary side. By raising the acquisition threshold of the evaluation circuit, an erroneous response of the evaluation circuit can be prevented, but at the same time the sensitivity of the evaluation circuit is also reduced. A second transmission pulse could also be sent after the decay of the interference which, however, would result in an increase in the signal run time.
Circuit configurations are known for driving the input coil of a magnetic transformer or a magnetically coupled coil pair in which each terminal of the input coil is connected to a power stage (for instance, using a full bridge circuit). Circuit configurations are also known in which only one terminal of the input coil is driven towards a fixed reference potential. Both circuit configurations can be operated both using direct current and alternating current. In the case of a direct current circuit, usually no capacitor is provided between the driver output and the terminal of the input coil, whereas in the case of an alternating circuit, a steady-state current flow through the input coil is prevented using a capacitor. Because of the decay of the current through the input coil caused by the charging of the capacitor, for each main pulse induced into the output coil, a counterpulse is created (a so-called backswing) having reverse polarity.